Hello,
I've just done a search for "Betteridge" on this site, and came across your 2005 quest to find John Betteridge of Whiteparish, Wiltshire.
I don't have a direct answer, but I'm researching my Betteridge roots in Sussex and Whiteparish sounded familiar. I searched my files and found from 1881 Census two Betteridge families in Eastbourne,Sussex and both families had Betteridge members born in Whiteparish.
I'm sure there is some link between those born in Whiteparish and those born in Eastbourne (possibly their grandparents or uncles), and between us we may have the answer.
Do you have any Betteridge links about 1800 to the Cotswolds area (Gloucestershire) ? My earliest Betteridge in Eastbourne is a John Betteridge married about 1807 in Eastbourne. I've found him on the 1841 Census - John Betteridge born about 1780 in Stow or Stoke in Gloucestershire ... but I can't find a baptism in Gloucestershire.
If you are still on the Betteridge search ... let me know.
John